CONSTRUCTING OREGON

The rock units and ages shown on this map tell a simplified story of the geologic history of Oregon. The units were assembled from the Oregon Geologic Data Compilation, a new digital geologic map of Oregon completed in 2009. The new map was made possible by digitizing 345 geologic maps with thousands of different geologic units and arranging the rock units by type and age. Having all of Oregon’s geology in one digital map makes it possible to organize rocks across the state into the major geologic layers that together have built the Oregon we see today. Each layer results from a major geologic event — some long-lived, some a geologic instant — that assembled the state like a complex building. With these layers, we can think of three phases of construction:

PHASE 1
FOUNDATION — Rocks many miles thick underlie the entire state and range from 400 million to 50 million years old.